Near-field light generating element comprising surface plasmon antenna with surface or edge opposed to waveguide

ABSTRACT

Provided is a near-field light generating element in which reduced is the propagation loss of excited surface plasmon that propagates to the near-field light generating end. The element comprises: a waveguide through which light for exciting surface plasmon propagates; and a plasmon antenna comprising a near-field light generating end and a propagation surface or edge. The propagation surface or edge extends to the near-field light generating end, and causes surface plasmon excited by the light to propagate thereon. Further, a portion of the side surface on the near-field light generating end side is opposed to the propagation surface or edge with a predetermined distance so as for the light to be coupled with the plasmon antenna in a surface plasmon mode. In this configuration, surface plasmon can propagates without significantly changing its wavenumber, which leads to a less propagation loss, and to an improved light use efficiency.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plasmon antenna for generating near-field light by being irradiated with light. And the present invention relates to a head used for thermally-assisted magnetic recording in which a magnetic recording medium is irradiated with near-field light, thereby anisotropic magnetic field of the medium is lowered, thus data can be written. Further, the present invention relates to a magnetic recording apparatus provided with the head.

2. Description of the Related Art

As the recording density of a magnetic disk apparatus becomes higher, further improvement has been required in the performance of a thin-film magnetic head and a magnetic recording medium. As the thin-film magnetic head, a composite-type thin-film magnetic head is widely used, which has a stacked structure of a magnetoresistive (MR) element for reading data and an electromagnetic transducer for writing data.

Whereas, the magnetic recording medium is generally a kind of discontinuous body of magnetic microparticles gathered together, and each of the magnetic microparticles has a single magnetic domain structure. Here, one record bit consists of a plurality of the magnetic microparticles. Therefore, in order to improve the recording density, it is necessary to decrease the size of the magnetic microparticles and reduce irregularity in the boundary of the record bit. However, the decrease in size of the magnetic microparticles raises a problem of degradation in thermal stability of the magnetization due to the decrease in volume. Recently, as a method for solving this problem of thermal stability, so-called a thermally-assisted magnetic recording technique is proposed, in which the magnetic recording medium is formed of a magnetic material with a large magnetic anisotropy energy K_(U), and writing is performed by reducing the anisotropic magnetic field with heat supplied to the magnetic recording medium just before applying write field.

As a thermally-assisted magnetic recording technique, a method has been generally known, in which a near-field light probe formed of a metal piece, so-called a plasmon antenna, is used for generating near-field light from plasmon that is excited by irradiated laser light. For example, U.S. Pat. No. 6,768,556B1 discloses a plasmon antenna that includes a metal scatterer with a strobilus shape formed on a substrate and a dielectric material film formed around the metal scatterer. And US Patent Publication No. 2004/081031 A1 discloses a configuration in which a plasmon antenna is formed in contact with the main magnetic pole of a magnetic head for perpendicular magnetic recording in such a way that the irradiated surface of the plasmon antenna is perpendicular to the surface of a magnetic recording medium. Further, US Patent Publication No. 2003/066944 A1 discloses a technique in which the tip of a plasmon antenna is made closer to a magnetic recording medium to attempt to irradiate the medium with stronger near-field light.

As described above, various thermally-assisted magnetic recording techniques have been proposed, which uses plasmon antennas. The present inventors have devised a near-field light generating element in which laser light propagating through a waveguide is coupled with a plasmon antenna in a surface plasmon mode to cause the excited surface plasmon to propagate to the opposed-to-medium surface, thereby providing near-field light, rather than directly applying the laser light to a plasmon antenna. The plasmon antenna in the element will be hereinafter referred to as a surface plasmon antenna. In the near-field light generating element, the temperature of the surface plasmon antenna does not excessively rise because laser light is not directly applied to the surface plasmon antenna. As a result, there can be avoided such a situation in which the end, which reaches the opposed-to-medium surface, of a read head element for reading data signal or servo signal from the magnetic recording medium becomes relatively far apart from the magnetic recording medium due to the thermal expansion of the plasmon antenna, which makes it difficult to properly read the servo signal. In addition, there can also be avoided such a situation in which the light use efficiency of the near-field light generating element is degraded because thermal disturbance of free electrons increases in the plasmon antenna. Here, the light use efficiency of a near-field light generating element is given by I_(OUT)/I_(IN)(×100), where I_(IN) is the intensity of laser light incident to the waveguide, and I_(OUT) is the intensity of near-field light emitted from a near-field light generating end of the plasmon antenna after converting the laser light into surface plasmon in the plasmon antenna.

The above-described near-field light generating element is required to have more improved light use efficiency. Actually, it is known that the light use efficiency of at least 10% or more is needed in order to achieve favorable thermally-assisted magnetic recording. To meet the requirement in the above-described surface plasmon antenna, especially, it is significantly important to reduce the propagation loss of excited surface plasmon that propagates to the near-field light generating end positioned on the opposed-to-medium surface.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a near-field light generating element in which reduced is the propagation loss of excited surface plasmon that propagates to the near-field light generating end, and the light use efficiency is improved.

Another object of the present invention is to provide a thermally-assisted magnetic recording head capable of appropriately heating the write position on the magnetic recording medium, to provide a head gimbal assembly (HGA) provided with the head, and further, to provide a magnetic recording apparatus provided with the HGA.

Some terms used in the specification will be defined before explaining the present invention. In a layered structure or an element structure formed on an element-formation surface of a slider substrate of the magnetic recording head according to the present invention, when viewed from a standard layer or element, a substrate side is defined as “lower” side, and the opposite side as an “upper” side. Further, “X-, Y- and Z-axis directions” are indicated in some figures showing embodiments of the head according to the present invention as needed. Here, Z-axis direction indicates above-described “up-and-low” direction, and +Z direction corresponds to a trailing side and −Z direction to a leading side. And Y-axis direction indicates a track width direction, and X-axis direction indicates a height direction.

Further, a “side surface” of a waveguide provided within the magnetic recording head is defined as an end surface other than the end surfaces perpendicular to the direction in which light propagates within the waveguide (−X direction), out of all the end surfaces surrounding the waveguide. According to the definition, an “upper surface” and a “lower surface” are one of the “side surfaces”. The “side surface” is a surface on which the propagating light can be totally reflected within the waveguide corresponding to a core.

According to the present invention, a near-field light generating element is provided, which comprises:

a waveguide through which a light for exciting surface plasmon propagates; and

a plasmon antenna comprising: a near-field light generating end for emitting near-field light; and a propagation surface or a propagation edge for causing surface plasmon excited by the light to propagate thereon, extending to the near-field light generating end, and

wherein a side surface of the waveguide extends to a neighborhood of the near-field light generating end, and a portion of the side surface on the near-field light generating end side is opposed to the propagation surface or the propagation edge with a predetermined distance so as for the light propagating through the waveguide to be coupled with the plasmon antenna in a surface plasmon mode.

In the above-described near-field light generating element, the propagation surface or the propagation edge of the surface plasmon antenna extends to the near-field light generating end, being opposed to a side surface of the waveguide. In this configuration, surface plasmon, which propagates on the propagation surface or the propagation edge and arrives at the near-field light generating end, can propagates without significantly changing its wavenumber during the propagation, which leads to a less propagation loss, and to an improved light use efficiency.

In the near-field light generating element according to the present invention, an inclined portion of the propagation surface or the propagation edge on the near-field light generating end side preferably extends so as to become closer to an end surface of the plasmon antenna toward the near-field light generating end, the end surface being on a side opposite to the propagation surface or the propagation edge. In this case, it is preferable that a first distance is 46% (percent) or more of a second distance, and 160% or less of the second distance, where the first distance denotes a distance between the inclined portion of the propagation surface or the propagation edge on the near-field light generating end side and the side surface of the waveguide, and the second distance denotes a distance between the portion other than the inclined portion of the propagation surface or the propagation edge and the side surface of the waveguide. Further, it is also preferable that the difference that is a result of subtracting the second distance from the first distance is −80 nm (nanometers) or more, and +90 nm or less. By the setting of the first and second distances, the light use efficiency of 10% or more can be obtained, which is required for achieving favorable thermally-assisted magnetic recording in the manufacturing field of the heads.

Further, in the near-field light generating element according to the present invention, the plasmon antenna is preferably formed of one element selected from a group of Pd, Pt, Rh, Ir, Ru, Au, Ag, Cu or Al, or an alloy made of at least two selected from the group. Furthermore, the propagation surface or the propagation edge is preferably covered with a material having a refractive index equal to or higher than a refractive index of a material covering a surface of the plasmon antenna, the surface being opposite to the propagation surface or the propagation edge. Further, it is preferable that a portion sandwiched between a portion of the side surface of the waveguide on the near-field light generating end side and the propagation surface or the propagation edge is a buffering portion having a refractive index lower than a refractive index of the waveguide. In this case, the buffering portion is also preferably a portion of an overcoat layer formed so as to cover the waveguide.

According to the present invention, a thermally-assisted magnetic recording head is provided, which comprises:

a magnetic pole for generating write field from its end on an opposed-to-medium surface side;

a waveguide through which a light for exciting surface plasmon propagates; and

a plasmon antenna comprising: a near-field light generating end for emitting near-field light, reaching the opposed-to-medium surface; and a propagation surface or a propagation edge for causing surface plasmon excited by the light to propagate thereon, extending to the near-field light generating end, and

wherein a side surface of the waveguide extends to a neighborhood of the near-field light generating end, and a portion of the side surface on the near-field light generating end side is opposed to the propagation surface or the propagation edge with a predetermined distance so as for the light propagating through the waveguide to be coupled with the plasmon antenna in a surface plasmon mode.

In the thermally-assisted magnetic recording head according to the present invention, the waveguide is preferably provided in a side opposite to the magnetic pole in relation to the plasmon antenna. Further, a portion on the opposed-to-medium surface side of the plasmon antenna is preferably inclined so as to become closer to an end portion on the opposed-to-medium surface side of the magnetic pole toward the opposed-to-medium surface. Furthermore, a portion on the opposed-to-medium surface side of the magnetic pole is preferably inclined so as to become closer to an end portion on the opposed-to-medium surface side of the plasmon antenna toward the opposed-to-medium surface. With these configurations, the waveguide can be sufficiently separated apart from the magnetic pole, while the near-field light generating end of the plasmon antenna is set to a position adjacent to the end surface on the opposed-to-medium surface side of the magnetic pole. Resultantly, there can be avoided such a situation in which a part of the light is absorbed into the magnetic pole, and the amount of light to be converted into near-field light is reduced. Further, it is preferable that a thermal conduction layer is provided between the plasmon antenna and the magnetic pole, so as to cover an end surface of the plasmon antenna, the surface being opposite to the propagation surface or the propagation edge.

According to the present invention, an HGA is further provided, which comprises: the above-described thermally-assisted magnetic recording head; and a suspension supporting the thermally-assisted magnetic recording head.

According to the present invention, a magnetic recording apparatus is further provided, which comprises: the above-described HGA; at least one magnetic recording medium; and a recording circuit for controlling write operations which the thermally-assisted magnetic recording head performs to the at least one magnetic recording medium, the recording circuit further comprising a light-emission control circuit for controlling operations of a light source that generates the light for exciting surface plasmon.

Further objects and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention as illustrated in the accompanying figures. In each figure, the same element as an element shown in other figure is indicated by the same reference numeral. Further, the ratio of dimensions within an element and between elements is arbitrary for viewability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view schematically illustrating a structure of a major part in one embodiment of a magnetic recording apparatus and an HGA according to the present invention;

FIG. 2 shows a perspective view illustrating one embodiment of thermally-assisted magnetic recording head according to the present invention;

FIG. 3 shows a cross-sectional view taken by plane A in FIG. 2, schematically illustrating a main part of the thermally-assisted magnetic recording head;

FIG. 4 shows a perspective view schematically illustrating the configuration of the waveguide, the surface plasmon antenna and the main magnetic pole layer;

FIG. 5 shows a perspective view illustrating the shapes of the end surfaces of the waveguide, the surface plasmon antenna and the electromagnetic transducer on the head part end surface;

FIG. 6 shows a schematic diagram for explaining the thermally-assisted magnetic recording utilizing the surface plasmon mode according to the present invention;

FIGS. 7 a to 7 d show schematic views illustrating various embodiments regarding the shape and arrangement of the near-field light generating element (the waveguide, the buffering portion and the surface plasmon antenna) and the main magnetic pole according to the present invention;

FIG. 8 shows a block diagram illustrating the circuit structure of the recording/reproducing and light-emission control circuit of the magnetic disk apparatus shown in FIG. 1;

FIG. 9 shows a graph illustrating the relationship between the first and second distances D_(WN1) and D_(WN2) and the light use efficiency shown in Table 1; and

FIGS. 10 a and 10 b show a cross-sectional view and a top view, respectively, schematically illustrating the structure of the bit-patterned medium used in the practical example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a perspective view schematically illustrating a structure of a major part in one embodiment of a magnetic recording apparatus and an HGA according to the present invention. Here, in the perspective view of the HGA, the side of the HGA, opposed to the surface of the magnetic recording medium, is presented as the upper side.

A magnetic disk apparatus as a magnetic recording apparatus shown in FIG. 1 includes: a plurality of magnetic disks 10 as magnetic recording media, rotating around a rotational axis of a spindle motor 11; an assembly carriage device 12 provided with a plurality of drive arms 14 thereon; a head gimbal assembly (HGA) 17 attached on the top end portion of each drive arm 14 and provided with a thermally-assisted magnetic recording head 21 as a thin-film magnetic head; and a recording/reproducing and light-emission control circuit 13 for controlling write/read operations of the thermally-assisted magnetic recording head 21 and further for controlling the emission operation of a laser diode as a light source that generates laser light for thermally-assisted magnetic recording, which will be described later.

In the present embodiment, the magnetic disk 10 is designed for perpendicular magnetic recording, and has a structure in which sequentially stacked on a disk substrate is: a soft-magnetic under layer; an intermediate layer; and a magnetic recording layer (perpendicular magnetization layer). The assembly carriage device 12 is a device for positioning the thermally-assisted magnetic recording head 21 above a track formed on the magnetic recording layer of the magnetic disk 10, on which recording bits are aligned. In the apparatus, the drive arms 14 are stacked in a direction along a pivot bearing axis 16 and can be angularly swung around the axis 16 by a voice coil motor (VCM) 15. The structure of the magnetic disk apparatus according to the present invention is not limited to that described above. For instance, the number of each of magnetic disks 10, drive arms 14, HGAs 17 and thermally-assisted magnetic recording heads 21 may be one.

Referring also to FIG. 1, a suspension 20 in the HGA 17 includes a load beam 200, a flexure 201 with elasticity fixed to the load beam 200, and a base plate 202 provided on the base portion of the load beam 200. Further, on the flexure 201, there is provided a wiring member 203 that is made up of lead conductors and connection pads electrically joined to both ends of the lead conductors. The thermally-assisted magnetic recording head 21 is fixed to the flexure 201 at the top end portion of the suspension 20 so as to face the surface of each magnetic disk 10 with a predetermined spacing (flying height). Moreover, one ends of the wiring member 203 are electrically connected to terminal electrodes of the thermally-assisted magnetic recording head 21. The structure of the suspension 20 is not limited to the above-described one. An IC chip for driving the head may be mounted midway on the suspension 20, though not shown.

FIG. 2 shows a perspective view illustrating one embodiment of thermally-assisted magnetic recording head 21 according to the present invention.

As shown in FIG. 2, a thermally-assisted magnetic recording head 21 is constituted of the slider 22 and the light source unit 23. The slider 22 includes: a slider substrate 220 formed of, for example, AlTiC (Al₂O₃—TiC), and having an air bearing surface (ABS) 2200 processed so as to provide an appropriate flying height; and a head part 221 formed on an element-formation surface 2202 perpendicular to the ABS 2200. While, the light source unit 23 includes: a unit substrate 230 formed of, for example, AlTiC (Al₂O₃—TiC), and having an joining surface 2300; and a laser diode 40 as a light source provided on a source-installation surface 2302 perpendicular to the joining surface 2300. The slider 22 and the light source unit 23 are bonded to each other so that the back surface 2201 of the slider substrate 220 and the joining surface 2300 of the unit substrate 230 have a surface contact with each other. Here, the back surface 2201 of the slider substrate 220 is defined as an end surface opposite to the ABS 2200 of the slider substrate 220. Alternatively, the thermally-assisted magnetic recording head 21 may have a configuration in which the laser diode 40 is provided directly on the slider 22 without using the light source unit 23.

In the slider 22, the head part 221 formed on the element-formation surface 2202 of the slider substrate 220 includes: a head element 32 constituted of a magnetoresistive (MR) element 33 for reading data from the magnetic disk and an electromagnetic transducer 34 for writing data to the magnetic disk; a waveguide 35 for guiding laser light generated from a laser diode 40 provided in the light source unit 23 to the opposed-to-medium surface side; a surface plasmon antenna 36 which, together with the waveguide 35, constitutes a near-field light generating element; an overcoat layer 38 formed on the element-formation surface 2202, so as to cover the MR element 33, the electromagnetic transducer 34, the waveguide 35, and the surface plasmon antenna 36; a pair of terminal electrodes 370 exposed in the upper surface of the overcoat layer 38 and electrically connected to the MR element 33; and a pair of terminal electrodes 371 also exposed in the upper surface of the overcoat layer 38 and electrically connected to the electromagnetic transducer 34. The terminal electrodes 370 and 371 are electrically connected to the connection pads of the wiring member 203 provided on the flexure 201 (FIG. 1).

One ends of the MR element 33, the electromagnetic transducer 34, and the surface plasmon antenna 36 reach the head part end surface 2210, which is an opposed-to-medium surface of the head part 221. Here, the head part end surface 2210 and the ABS 2200 constitute the whole opposed-to-medium surface of the thermally-assisted magnetic recording head 21. During actual write and read operations, the thermally-assisted magnetic recording head 21 aerodynamically flies above the surface of the rotating magnetic disk with a predetermined flying height. Thus, the ends of the MR element 33 and electromagnetic transducer 34 face the surface of the magnetic recording layer of the magnetic disk with an appropriate magnetic spacing. Then, the MR element 33 reads data by sensing signal magnetic field from the magnetic recording layer, and the electromagnetic transducer 34 writes data by applying signal magnetic field to the magnetic recording layer. When writing data, laser light is generated from the laser diode 40 of the light source unit 23 and propagates through the waveguide 35. Then, the laser light is coupled with the surface plasmon antenna 36 in a surface plasmon mode, and causes surface plasmon to be excited on the surface plasmon antenna 36. The surface plasmon propagates on a propagation edge or a propagation surface provided in the surface plasmon antenna 36, which will be detailed later, toward the head part end surface 2210, which causes near-field light to be generated from the end on the head part end surface 2210 side of the surface plasmon antenna 36. The generated near-field light reaches the surface of the magnetic disk, and heats a portion of the magnetic recording layer of the magnetic disk. As a result, the anisotropic magnetic field (coercive force) of the portion is decreased to a value that enables writing; thus the thermally-assisted magnetic recording can be accomplished.

FIG. 3 shows a cross-sectional view taken by plane A in FIG. 2, schematically illustrating a main part of the thermally-assisted magnetic recording head 21.

As shown in FIG. 3, the MR element 33 is formed on the insulating layer 380 stacked on the element-formation surface 2202, and includes: an MR multilayer 332; and a lower shield layer 330 and an upper shield layer 334 which sandwich the MR multilayer 332 and the insulating layer 381 therebetween. The upper and lower shield layers 334 and 330 prevent the MR multilayer 332 from receiving external magnetic field as a noise. The upper and lower shield layers 334 and 330 are magnetic layers formed of soft-magnetic materials such as NiFe (Permalloy), FeSiAl (Sendust), CoFeNi, CoFe, FeN, FeZrN or CoZrTaCr, or the multilayer of at least two of these materials, with thickness of approximately 0.5 to 3 μm (micrometers), by using a frame plating method or a sputtering method.

The MR multilayer 332 is a magneto-sensitive part for detecting signal magnetic field by using MR effect. The MR multilayer 332 may be, for example: a current-in-plane giant magnetoresistive (CIP-GMR) multilayer that utilizes CIP-GMR effect; a current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) multilayer that utilizes CPP-GMR effect; or a tunnel magnetoresistive (TMR) multilayer that utilizes TMR effect. The MR multilayer 332 that utilizes any MR effect described above can detect signal magnetic field from the magnetic disk with high sensitivity. In the case that the MR multilayer 332 is a CPP-GMR multilayer or a TMR multilayer, the upper and lower shield layers 334 and 330 act as electrodes. Whereas, in the case that the MR multilayer 332 is a CIP-GMR multilayer, insulating layers are provided between the MR multilayer 332 and respective upper and lower shield layers 334 and 330; further, formed are MR lead layers that is electrically connected to the MR multilayer 332.

Also as shown in FIG. 3, the electromagnetic transducer 34 is designed for perpendicular magnetic recording, and includes a main magnetic pole layer 340, a gap layer 341, a write coil layer 343, a coil insulating layer 344, and a write shield layer 345.

The main magnetic pole layer 340 is provided on an insulating layer 384 made of an insulating material such as Al₂O₃ (alumina), and acts as a magnetic path for converging and guiding a magnetic flux toward the magnetic recording layer (perpendicular magnetization layer) of the magnetic disk, the magnetic flux being excited by write current flowing through the write coil layer 343. The main magnetic pole layer 340 has a structure in which a main magnetic pole 3400 and a main pole body 3401 are sequentially stacked. The main magnetic pole 3400 includes: a first main pole portion 3400 a having a small width W_(P) (FIG. 5) in the track width direction; and a second main pole portion 3400 b located on the first main pole portion 3400 a and at the rear (+X side) of the portion 3400 a. The small width W_(P) of the first main pole portion 3400 a enables a fine write magnetic field to be generated, so that the track width can be set to be a very small value adequate for higher recording density. The main magnetic pole 3400 is formed of a soft-magnetic material with saturation magnetic flux density higher than that of the main pole body 3401, which is, for example, an iron alloy containing Fe as a main component, such as FeNi, FeCo, FeCoNi, FeN or FeZrN. The thickness of the first main pole portion 3400 a is, for example, in the range of approximately 0.1 to 0.8 μm.

The gap layer 341 forms a gap provided for separating the main magnetic pole layer 340 from the write shield layer 345 in the region near the head part end surface. The gap layer 341 is formed, for example, of a non-magnetic insulating material such as Al₂O₃ (alumina), SiO₂ (silicon dioxide), AlN (aluminum nitride) or DLC, or formed of a non-magnetic conductive material such as Ru (ruthenium). The thickness of the gap layer 341 determines the distance between the main magnetic pole layer 340 and the write shield layer 345, and is, for example, in the range of approximately 0.01 to 0.5 μm. The write coil layer 343 is formed on a insulating layer 3421 made of an insulating material such as Al₂O₃ (alumina), in such a way to pass through in one turn at least between the main magnetic pole layer 340 and the write shield layer 345, and has a spiral structure with a back contact portion 3402 as a center. The write coil layer 343 is formed of a conductive material such as Cu (copper). The write coil layer 343 is covered with a coil insulating layer 344 that is formed of an insulating material such as a heat-cured photoresist and electrically isolates the write coil layer 343 from the main magnetic pole layer 340 and the write shield layer 345. The write coil layer 343 has a monolayer structure in the present embodiment, however, may have a two or more layered structure or a helical coil shape. Further, the number of turns of the write coil layer 343 is not limited to that shown in FIG. 3, and may be, for example, in the range from two to seven.

The write shield layer 345 reaches the head part end surface 2210, and acts as a magnetic path for the magnetic flux returning from a soft-magnetic under layer that is provided under the magnetic recording layer (perpendicular magnetization layer) of the magnetic disk. The thickness of the write shield layer 345 is, for example, approximately 0.5 to 5 μm. Further, the write shield layer 345 has a trailing shield 3450 that is a portion opposed to the main magnetic pole layer 340. The trailing shield 3450 also extends to the head part end surface 2210, and is provided for receiving the magnetic flux spreading from the main magnetic pole layer 340. In the present embodiment, the trailing shield 3450 has a width in the track width direction larger than the width of the main pole body 3401 as well as than the first main pole portion 3400 a. This trailing shield 3450 causes the magnetic field gradient between the end portion of the trailing shield 3450 and the first main pole portion 3400 a to become steeper. As a result, a jitter of signal output becomes smaller, and therefore, error rates during read operation can be reduced. The write shield layer 345 is formed of a soft-magnetic material; especially, the trailing shield 3450 is formed of a material with high saturation magnetic flux density such as NiFe (Permalloy) or formed of an iron alloy as the main magnetic pole 3400 is formed of.

Referring also to FIG. 3, the waveguide 35 and the surface plasmon antenna 36 are provided between the MR element 33 and the electromagnetic transducer 34, and constitute a near-field light generating element as an optical system within the head part 221. Here, the waveguide 35 is arranged in parallel with the element-formation surface 2202, and extends from an end surface 352 reaching the head part end surface 2212 to an end surface 350 on the head part end surface 2210 side. A portion of the upper surface (side surface) of the waveguide 35 faces a portion of the lower surface (including a propagation edge 360 (FIG. 4) or a propagation surface) of the surface plasmon antenna 36 with a predetermined distance, and the sandwiched portion between these portions constitutes a buffering portion 50 having a refractive index lower than that of the waveguide 35. The buffering portion 50 acts for coupling the laser light that propagates through the waveguide 35 with the surface plasmon antenna 36 in the surface plasmon mode. Here, the buffering portion 50 may be a portion of an insulating layer 384 that is a part of the overcoat layer 38, or a new layer provided other than the insulating layer 384. A detailed description of the waveguide 35, the surface plasmon antenna 36, and the buffering portion 50 will be given later with reference to FIG. 4.

Further, in the present embodiment, an inter-element shield layer 39 is provided between the MR element 33 and the electromagnetic transducer 34 (waveguide 35), sandwiched by the insulating layers 382 and 383. The inter-element shield layer 39 may be formed of soft-magnetic material, and plays a role for shielding the MR element 33 from the magnetic field generated from the electromagnetic transducer 34. Further, a backing coil portion may be provided between the inter-element shield layer 39 and the waveguide 35, though not shown in the figure. The backing coil portion is a coil portion for generating magnetic flux to negate a magnetic flux loop that is generated from the electromagnetic transducer 34 and passes through the upper and lower shield layers 334 and 330 of the MR element 33. Thus, the backing coil portion intends to suppress wide adjacent track erasure (WATE), that is, unwanted writing or erasing to the magnetic disk.

Also according to FIG. 3, the light source unit 23 includes: a unit substrate 230; a laser diode 40 provided on the source-installation surface 2302 of the unit substrate 230; a terminal electrode 410 electrically connected to the lower surface 401 as an electrode of the laser diode 40; and a terminal electrode 411 electrically connected to the upper surface 403 as an electrode of the laser diode 40. The terminal electrodes 410 and 411 are electrically connected to the connection pads of the wiring member 203 provided on the flexure 201 (FIG. 1). By applying a predetermined voltage between both electrodes 410 and 411 of the laser diode 40, laser light is emitted from the emission center on an emission surface 400 of the laser diode 40. Here, in the configuration of the head as shown in FIG. 3, the oscillation of electric field component of the laser light generated from the laser diode 40 preferably has a direction perpendicular to the stacking surface of the active layer 40 e (a Z-axis direction). That is, the laser diode 40 preferably generates a laser light with TM polarization. This enables the laser light propagating through the waveguide 35 to be coupled with the surface plasmon antenna 36 through the buffering portion 50 in the surface plasmon mode.

A light source such as InP base, GaAs base or GaN base diode can be utilized as the laser diode 40, which is usually used for communication, optical disk storage or material analysis. The wavelength λ_(L) of the radiated laser light may be, for example, in the range of approximately 375 nm to 1.7 μm (micrometer). Specifically, for example, a laser diode of InGaAsP/InP quaternary mixed crystal can also be used, in which possible wavelength region is set to be from 1.2 to 1.67 μm. The laser diode 40 has a multilayered structure including an upper-electrode 40 a, an active layer 40 e, and a lower-electrode 40 i. On the front and rear cleaved surfaces of the multilayered structure of the laser diode 40, respectively formed are reflective layers made of, for example, SiO₂ or Al₂O₃ for exciting the oscillation by total reflection. Further, the reflective layer 42 has an opening in the position of the active layer 40 e including the light-emission center 4000. Here, the laser diode 40 has, for example, a thickness T_(LA) of approximately 60 to 200 μm.

Further, an electric source provided within the magnetic disk apparatus can be used for driving the laser diode 40. In fact, the magnetic disk apparatus usually has an electric source with applying voltage of, for example, approximately 2V, which is sufficient for the laser oscillation. The amount of electric power consumption of the laser diode 40 is, for example, in the order of several tens mW, which can be covered sufficiently by the electric source provided within the magnetic disk apparatus. In practice, a predetermined voltage is applied between the terminal electrode 410 connected electrically to the lower-electrode 40 i and the terminal electrode 411 connected electrically to the upper-electrode 40 a by using the electric source, to oscillate the laser diode 40. Then, laser light radiates from the opening including the emission center 4000 of the reflective layer 42.

The laser diode 40 and terminal electrodes 410 and 411 are not limited to the above-described embodiment. Further, alternatively, the thermally-assisted magnetic recording head 21 may include no laser diode 40; then, the light-emission center of a laser diode provided within the magnetic disk apparatus and the end surface 352 of the waveguide 35 may be connected by using optical fiber.

By joining the above-described slider 22 and light source unit 23, constituted is the thermally-assisted magnetic recording head 21. In the joining, the joining surface 2300 of the unit substrate 230 is made having a surface contact with the back surface 2201 of the slider substrate 220. Then, the locations of the unit substrate 230 and the slider substrate 220 are determined so that the laser light generated from the laser diode 40 can directly enter the waveguide 35 through the end surface 352 opposite to the ABS 2200 of the waveguide 35.

Each of the slider 22 and light source unit 23 may have an arbitrary size. For example, the slider 22 may be so-called a femto slider in which the width in the track width direction (Y-axis direction) is 700 μm; the length (in Z-axis direction) is 850 μm; and the thickness (in X-axis direction) is 230 μm. In the case, the light source unit 23 may be one size smaller than the slider 22, for example, in which the width in the track width direction is 425 μm; the length is 300 μm; and the thickness is 300 μm.

FIG. 4 shows a perspective view schematically illustrating the configuration of the waveguide 35, the surface plasmon antenna 36 and the main magnetic pole layer 340. In the figure, the head part end surface 2210 is positioned at the left side, the end surface 2210 including positions where write field and near-field light are emitted toward the magnetic recording medium.

Referring to FIG. 4, the configuration includes the waveguide 35 for propagating laser light 53 used for generating near-field light, and the surface plasmon antenna 36 that has a propagation edge 360 as an edge on which surface plasmon excited by the laser light 53 propagates. The surface plasmon antenna 36 has a near-field light generating end surface 36 a reaching the head part end surface 2210. Further, a buffering portion 50 is provided as a portion sandwiched between a portion of the side surface 354, that is, the side surfaces 3540 and 3541 of the waveguide 35 and the lower surface 362 including a propagation edge 360 of the surface plasmon antenna 36, the propagation edge 360 being opposed to the side surfaces 3540 and 3541. That is, the propagation edge 360 is covered with the buffering portion 50, and both ends of the propagation edge 360 and the buffering portion 50 reach the head part end surface 2210. The buffering portion 50 acts for coupling the laser light 53 with the surface plasmon antenna 36 in the surface plasmon mode. And the propagation edge 360 plays a role of propagating surface plasmon excited by the laser light 53 to the near-field light generating end surface 36 a. Here, a side surface of the waveguide 35 indicates, out of end surfaces surrounding the waveguide 35, end surfaces other than the end surface 350 on the head part end surface 2210 side and the end surface 352 on the opposite side, these end surfaces 350 and 352 being perpendicular to the propagating direction (−X direction) of the laser light 53. The side surface serves as a surface on which the propagating laser light 53 can be totally reflected in the waveguide 35 that corresponds to a core. In the present embodiment, the side surface 354 of the waveguide 35, a portion of which is in surface contact with the buffering portion 50, is the upper surface of the waveguide 35. The buffering portion 50 may be a portion of the overcoat layer 38 (FIG. 2) or a new layer provided other than the overcoat layer 38.

Further, the near-field light generating end surface 36 a of the surface plasmon antenna 36 is close to an end surface 3400 e of the main magnetic pole 3400, the end surface 3400 e reaching the head part end surface 2210. Moreover, the propagation edge 360 extends to the near-field light generating end surface 36 a, the edge 360 being opposed to the side surface 354 of the waveguide 35 with a predetermined distance through the buffering portion 50. Resultantly, the side surface 354 of the waveguide 35 reaches the neighborhood of the near-field light generating end surface 36 a. Further, a portion of the propagation edge 360 on the end surface 36 a side (end surface 2210 side) has a shape of line or curve extending so as to become closer to the end surface 361 on the side opposite to the propagation edge 360 of the plasmon antenna 36 toward the near-field light generating end surface 36 a. The propagation edge 360 can be made rounded to prevent surface plasmon from running off from the edge 360. The curvature radius of the rounded edge may be, for example, in the range of 5 to 500 nm.

Here, the first distance D_(WN1) denotes a distance between the inclined portion 3600 on the end surface 36 a side of the propagation edge 360 and the side surface 3540 of the waveguide 35. And the second distance D_(WN2) denotes a distance between the portion 3601 other than the inclined portion 3600 of the propagation edge 360 and the side surface 3541 of the waveguide 35. As explained in detail with practical examples later, the first distance D_(WN1) is preferably 46% (percent) or more of the second distance D_(WN2), and 160% or less of the second distance D_(WN2). Further, the difference (D_(WN1)-D_(WN2)), which is the result of subtracting the second distance D_(WN2) from the first distance D_(WN1), is preferably −80 nm or more, and +90 nm or less. The setting of the distances D_(WN1) and D_(WN2) enables the light use efficiency of the near-field light generating element to be 10% or more, the near-field light generating element including the waveguide 35, the buffering portion 50 and the plasmon antenna 36, as detailed later.

Further, in the present embodiment, the surface plasmon antenna 36 tapers toward the near-field light generating end surface 36 a in the height direction (Z-axis direction) near the head part end surface 2210. And the surface plasmon antenna 36 has a cross-section taken by YZ plane with a triangular shape, and especially has a predetermined triangular shape in the vicinity of the head part end surface 2210. As a result, in the present embodiment, the near-field light generating end surface 36 a has a triangular shape (FIG. 5) in which one apex is the end of the propagation edge 360 reaching the end surface 36 a. Here, surface plasmon propagating on the propagation edge 360 reaches the near-field light generating end surface 36 a, and then causes near-field light to be generated from the end surface 36 a.

The waveguide 35 and the buffering portion 50 are provided in −Z direction side, that is, in the side opposite to the main magnetic pole 3400 in relation to the surface plasmon antenna 36. As a result, the propagation edge 360, which is covered with the buffering portion 50, is also positioned on the side opposite to the main magnetic pole 3400 in the surface plasmon antenna 36. With such a configuration, even when a distance between the end surface 3400 e for generating write field in the main magnetic pole 3400 and the near-field light generating end surface 36 a for emitting near-field light is sufficiently small, preferably 100 nm or less, the waveguide 35 can be sufficiently separated apart from the main magnetic pole 3400 and the main pole body 3401. Resultantly, there can be avoided such a situation in which a part of the laser light 53 is absorbed into the main magnetic pole 3400 and main pole body 3401 made of metal and the amount of light to be converted into the near-field light is reduced.

Also as shown in FIG. 4, the waveguide 35 may have a rectangular parallelepiped shape, or may have a portion on the head part end surface 2210 side, which has a narrower width in the track width direction (Y-axis direction). The width W_(WG1) in the track width direction (Y-axis direction) of a portion on the side of the end surface opposite to the head part end surface 2210 of the waveguide 35 may be, for example, in the range approximately from 0.5 to 200 μm (micrometers). The width W_(WG2) in the track width direction (Y-axis direction) of a portion on the end surface 350 side of the waveguide 35 may be, for example, in the range approximately from 0.3 to 100 μm. And the thickness T_(WG) (in Z-axis direction) may be, for example, in the range approximately from 0.1 to 4 μm, and the height (length) H_(WG) (in X-axis direction) may be, for example, in the range approximately from 10 to 300 μm.

Further, the side surfaces of the waveguide 35: the upper surface 354; the lower surface 353; and both the side surfaces 351 in the track width direction (Y-axis direction) have a contact with the overcoat layer 38 (FIG. 2) except the portion having a surface contact with the buffering portion 50. Here, the waveguide 35 is formed of a material with refractive index n_(WG) higher than refractive index n_(OC) of the constituent material of the overcoat layer 38, made by using, for example, a sputtering method. For example, in the case that the wavelength λ_(L) of laser light is 600 nm and the overcoat layer 38 is formed of SiO₂ (n=1.5), the waveguide 35 can be formed of, for example, Al₂O₃ (n=1.63). Further, in the case that the overcoat layer 38 is formed of Al₂O₃ (n=1.63), the waveguide 35 can be formed of, for example, SiO_(X)N_(Y) (n=1.7−1.85), Ta₂O₅ (n=2.16), Nb₂O₅ (n=2.33), TiO (n=2.3−2.55) or TiO₂ (n=2.3−2.55). This material structure of the waveguide 35 enables the propagation loss of laser light 53 to be reduced due to the excellent optical characteristics of the constituent material. Further, the waveguide 35 can provide the total reflection in all the side surfaces due to the existence of the overcoat layer 38 as a clad. As a result, more amount of laser light 53 can reach the position of the buffering portion 50, which improves the propagation efficiency of the waveguide 35.

Further, alternatively, the waveguide 35 may have a multilayered structure of dielectric materials in which the upper a layer is, the higher becomes the refractive index n of the layer. The multilayered structure can be realized, for example, by sequentially stacking dielectric materials of SiO_(X)N_(Y) with the composition ratios X and Y appropriately changed. The number of stacked layers may be, for example, in the range from 8 to 12. In the case that laser light 53 has a linear polarization in Z-axis direction, the above-described structure enables the laser light 53 to propagate in the position closer to the buffering portion 50. In this case, by choosing the composition and layer thickness in each layer, and the number of layers of the multilayered structure, the laser light 53 can propagate in the desired position in Z-axis direction.

The surface plasmon antenna 36 is preferably formed of a conductive material of, for example, metal such as Pd, Pt, Rh, Ir, Ru, Au, Ag, Cu or Al, or an alloy made of at least two of these elements. Further, the surface plasmon antenna 36 can have a width W_(NF) in the track width direction (Y-axis direction) sufficiently smaller than the wavelength of the laser light 53, for example, of approximately 10 to 100 nm. And the surface plasmon antenna 36 can have a thickness T_(NF1) (in Z-axis direction) sufficiently smaller than the wavelength of the laser light 53, for example, of approximately 10 to 100 nm. Further, the length (height) H_(NF) (in X-axis direction) can be set to be, for example, in the range of, approximately, 0.8 to 6.0 μm.

The buffering portion 50 is formed of a dielectric material having refractive index n_(BF) lower than the refractive index n_(WG) of the waveguide 35. For example, when the wavelength λ_(L) of laser light is 600 nm and the waveguide 35 is formed of Al₂O₃ (n=1.63), the buffering portion 50 may be formed of SiO₂ (n=1.46). Further, when the waveguide 35 is formed of Ta₂O₅ (n=2.16), the buffering portion 50 may be formed of SiO₂ (n=1.46) or Al₂O₃ (n=1.63). In these cases, the buffering portion 50 can be a portion of the overcoat layer 38 (FIG. 2) serving as a clad made of SiO₂ (n=1.46) or Al₂O₃ (n=1.63).

Further, the length L_(BF2) (in X-axis direction) of a portion of the buffering portion 50, the portion being sandwiched between the side surface 3541 of the waveguide 35 and the propagation edge 3601, is preferably in the range of 0.5 to 5 μm. Furthermore, the length (L_(BF1)+L_(BF2)) of the whole buffering portion 50, that is, the portion through which the waveguide 35 and the surface plasmon antenna 36 are coupled with each other in a surface plasmon mode, is preferably larger than the wavelength λ_(L) of the laser light 53. In this preferable case, the coupled portion has an area markedly larger than a so-called “focal region” in the case that, for example, laser light is converged on a buffering portion 50 and a surface plasmon antenna 36 and coupled in a surface plasmon mode. As a result, very stable coupling in the surface plasmon mode can be achieved. The thickness of a portion of the buffering portion 50 in the direction perpendicular to the side surface 3540, the portion being sandwiched between the side surface 3540 and the inclined portion 3600 of the propagation edge, is equivalent to the above-described first distance D_(WN1), and the thickness of a portion of the buffering portion 50 in the direction perpendicular to the side surface 3541, the portion being sandwiched between the side surface 3541 and the propagation edge 3601, is equivalent to the above-described second distance D_(WN2). The length L_(BF1), L_(BF2) and the thickness (D_(WN1) and D_(WN2)) are important parameters for obtaining proper excitation and propagation of surface plasmon.

Also as shown in FIG. 4, a thermal conduction layer 51 is preferably provided on the head part end surface 2210 side between the surface plasmon antenna 36 and the first main pole portion 3400 a. The thermal conduction layer 51 is formed of, for example, an insulating material such as AlN, SiC or DLC, which has higher thermal conductivity compared with that of the overcoat layer 38 (FIG. 2). The arrangement of such a thermal conduction layer 51 allows a part of the heat generated when the surface plasmon antenna 36 emits near-field light to get away to the main magnetic pole 3400 and the first main pole portion 3400 a through the thermal conduction layer 51. That is, the main magnetic pole 3400 and the first main pole portion 3400 a can be used as a heatsink. Resultantly, excessive temperature rise of the surface plasmon antenna 36 can be suppressed, and there can be avoided unwanted protrusion of the near-field light generating end surface 36 a and substantial reduction in the light use efficiency of the surface plasmon antenna 36.

The thickness T_(TC) of the thermal conduction layer 51 is equivalent to a distance D_(N-P) (FIG. 5) between the near-field light generating end surface 36 a and the end surface 3400 e of the main magnetic pole 3400, and is set to be a small value of 100 nm or less. Further, the refractive index n_(IN) of the thermal conduction layer 51 is set equal to or lower than the refractive index n_(BF) of the buffering portion that covers the propagation edge 360 of the surface plasmon antenna 36. That is, the propagation edge 360 of the surface plasmon antenna 36 is covered with a material having a refractive index n_(BF) equal to or higher than the refractive index n_(IN) of a material covering the end surface 361 opposite to the edge 360. This allows surface plasmon to propagate stably on the propagation edge 360. It is known to be preferable in practice to satisfy the relation of refractive index n_(BF)≦refractive index n_(IN)×1.5.

Also according to FIG. 4, the main magnetic pole layer 340 includes, as described-above, the main magnetic pole 3400 and the main pole body 3401. The main magnetic pole 3400 includes; the first main pole portion 3400 a having the end surface 3400 e reaching the head part end surface 2210; and the second main pole portion 3400 b, the end portion on the head part end surface 2210 side of the portion 3400 b being overlapped on a portion, on the side opposite to the end surface 2210, of the first main pole portion 3400 a. Further, the end portion on the head part end surface 2210 side of the main pole body 3401 is overlapped on a portion, on the side opposite to the end surface 2210, of the second main pole portion 3400 b. Namely, the end portion on the head part end surface 2210 side of the main magnetic pole layer 340 has a shape extending slantwise relative to the element-formation surface 2202 (FIG. 3) toward the end portion on the head part end surface 2210 side of the surface plasmon antenna 36. As a result, the end surface 3400 e of the main magnetic pole layer 340 can be made sufficiently close to the near-field light generating end surface 36 a, under the condition that the main magnetic pole layer 340 is sufficiently separated apart from the waveguide 35.

FIG. 5 shows a perspective view illustrating the shapes of the end surfaces of the waveguide 35, the surface plasmon antenna 36 and the electromagnetic transducer 34 on the head part end surface 2210. The front face of the figure is the head part end surface 2210.

As shown in FIG. 5, the main magnetic pole 3400 (the first main pole portion 3400 a) and the write shield layer 345 (the trailing shield 3450) of the electromagnetic transducer 34 reach the head part end surface 2210. The shape of the end surface of the main magnetic pole 3400 on the head part end surface 2210 is, for example, a rectangle, a square or a trapezoid. Here, the above-described width W_(P) is a length of the edge on the leading side of the end surface 3400 e of the main magnetic pole 3400, and provides the width of a track formed on the magnetic recording layer of the magnetic disk in the case of magnetic-field-dominant recording. The width W_(P) can be, for example, in the range of approximately 0.05 to 0.5 μm.

Moreover, on the head part end surface 2210, the near-field light generating end surface 36 a of the surface plasmon antenna 36 is positioned close to the end surface 3400 e of the main magnetic pole 3400 and in the leading side (−Z direction side) of the end surface 3400 e. Here, a distance D_(N-P) between the near-field light generating end surface 36 a and the end surface 3400 e is set to be a sufficiently small value of, for example, 100 nm or less. In the thermally-assisted magnetic recording according to the present invention, the near-field light generating end surface 36 a functions as a main heating action part, and the end surface 3400 e functions as a writing action part. Therefore, by setting the distance D_(N-P) in the above-described way, the write field with sufficiently large gradient can be applied to a portion of the recording layer of the magnetic disk, which has been sufficiently heated. This enables a stable thermally-assisted write operation to be securely achieved.

Furthermore, in the present embodiment, the near-field light generating end surface 36 a has a shape of isosceles triangle on the head part end surface 2210, having a bottom edge 361 a on the trailing side (+Z side) and an apex on the leading side (−Z side) that is an end 360 a of the propagation edge 360. The height T_(NF2) of the near-field light generating end surface 36 a (the thickness of the surface plasmon antenna 36 on the head part end surface 2210) is preferably 30 nm or less, and more preferably 20 nm or less. Thereby, the near-field-light emitting position on the end surface 36 a can become close to the edge 361 a on the trailing side, that is, closer to the end surface 3400 e of the main magnetic pole 3400.

Further, a distance D_(W-P) between the waveguide 35 and the main magnetic pole 3400 is made sufficiently large while the distance D_(N-P) is set to a minute value as described above. That is, with the structure according to the present invention shown in FIG. 4, the waveguide 35 can be sufficiently separated apart from the main magnetic pole 3400 and the main pole body 3401. Resultantly, there can be avoided such a situation in which a part of the laser light is absorbed into the main magnetic pole 3400 or the main pole body 3401 made of metal and the amount of light to be converted into near-field light is reduced.

Referring also to FIG. 5, the near-field light generating end surface 36 a and the end surface 350 of the waveguide 35, which is in the leading side (−Z side) of the end surface 36 a, are positioned so as to sandwich the end surface 50 a of the buffering portion 50 therebetween. Therefore, the side surface 354 of the waveguide 35 extends to the neighborhood of the near-field light generating end surface 36 a, while being opposed to the propagation edge 360 of the surface plasmon antenna 36. In this configuration, surface plasmon, which propagates through the propagation edge 360 and reaches the end surface 36 a, can propagates without significantly changing its wavenumber K_(SP) on the portion 3601 and inclined portion 3600 of the propagation edge and on their boundary, which leads to a less propagation loss.

FIG. 6 shows a schematic diagram for explaining the thermally-assisted magnetic recording utilizing the surface plasmon mode according to the present invention.

Referring to FIG. 6, when the electromagnetic transducer 34 writes data onto the recording layer of the magnetic disk 10, first, laser light 53 emitted from the laser diode 40 of the light source unit 23 propagates through the waveguide 35. Next, the laser light 53, which has advanced to near the buffering portion 50, couples with the optical configuration including the waveguide 35 with a refractive index n_(WG), the buffering portion 50 with a refractive index n_(BF) and the surface plasmon antenna 36 made of conductive material such as metal, and induces the surface plasmon mode on the propagation edge 360 of the surface plasmon antenna 36. That is, the laser light couples with the surface plasmon antenna 36 in the surface plasmon mode. Actually, evanescent light is excited within the buffering portion 50 based on an optical boundary condition between the waveguide 35 as a core and the buffering portion 50. Then, the evanescent light couples with the fluctuation of electric charge excited on the metal surface (propagation edge 360) of the surface plasmon antenna 36, and induces the surface plasmon mode, and thus surface plasmon is excited. To be exact, there excited is surface plasmon polariton in this system because surface plasmon as elementary excitation is coupled with an electromagnetic wave. However, the surface plasmon polariton will be hereinafter referred to as surface plasmon for short.

The propagation edge 360 is located closest to the waveguide 35 on the inclined lower surface 362 of the surface plasmon antenna 36, and is just an edge where electric field tends to converge and thus surface plasmon can easily be excited. However, as described later, the surface plasmon antenna may alternatively have a propagation surface on which surface plasmon is excited and propagates.

In the induced surface plasmon mode, surface plasmon 60 is excited on the propagation edge 360 of the plasmon antenna 36, and propagates in the direction shown by arrows 61 on the edge 360. The propagation of the surface plasmon 60 can occur under the condition that the propagation edge 360 is covered with the buffering portion 50 having a refractive index n_(BF) equal to or higher than a refractive index n_(IN) of the material covering the end surface 361 of the surface plasmon antenna 36 on the side opposite to the edge 360. It is known to be preferable in practice to satisfy the relation of refractive index n_(BF)=refractive index n_(IN)×1.5.

By the above-described propagation of the surface plasmon 60, the surface plasmon 60, namely, electric field converges on the near-field light generating end surface 36 a that reaches the head part end surface 2210 and includes the apex 36 a that is the destination of the propagation edge 360. As a result, near-field light 62 is emitted from the near-field light generating end surface 36 a. The near-field light 62 is radiated toward the magnetic recording layer of the magnetic disk 10, and reaches the surface of the magnetic disk 10 to heat a portion of the magnetic recording layer of the magnetic disk 10. This heating reduces the anisotropic magnetic field (coercive force) of the portion to a value with which write operation can be performed. Immediately after the heating, write field 63 generated from the main magnetic pole 3400 is applied to the portion to perform write operation. Thus, a thermally-assisted magnetic recording can be achieved.

In the magnetic recording, by adjusting the shape and size of the near-field light generating end surface 36 a on the head part end surface 2210, the emitting position of near-field light 62 on the end surface 36 a can be set to be closer to the first main pole portion 3400 a on the trailing side (on the edge 361 a side). In the case, write field with sufficiently large gradient can be applied to a portion of the magnetic recording layer of the magnetic disk 10, which has been sufficiently heated. This enables a stable thermally-assisted write operation to be securely achieved.

Further, in a conventional case in which a plasmon antenna provided on the end surface of a head is directly irradiated with the laser light propagating through a waveguide, most of the irradiating laser light has been converted into thermal energy within the plasmon antenna. In this case, the size of the plasmon antenna has been set smaller than the wavelength of the laser light, and its volume is very small. Therefore, the plasmon antenna has been brought to a very high temperature, for example, 500° C. (degrees Celsius) due to the thermal energy. On the contrary, in the thermally-assisted magnetic recording according to the present invention, the surface plasmon mode is used, and the near-field light 62 is generated by propagating the surface plasmon 60 toward the head part end surface 2210. This brings the temperature at the near-field light generating end surface 36 a to, for example, about 100° C. during the emission of near-field light, which is greatly reduced compared to the conventional. This reduction of temperature resultantly allows the protrusion of the near-field light generating end surface 36 a toward the magnetic disk 10 to be suppressed; thereby favorable thermally-assisted magnetic recording can be achieved.

Referring also to FIG. 6, the above-described surface plasmon mode can be induced by setting the refractive index n_(BF) of the buffering portion 50 to be lower than the refractive index n_(WG) of the waveguide 35 (n_(BF)<n_(WG)). Here, the propagation edge 360 of the surface plasmon antenna 36 extends to the apex 360 a of the near-field light generating end surface 36 a, while being opposed to the side surface 354 of the waveguide 35. In this configuration, surface plasmon, which propagates through the propagation edge 360 and reaches the end surface 36 a, can propagates without significantly changing its wavenumber K_(SP) on the portion 3601 and inclined portion 3600 of the propagation edge and on their boundary, which leads to a less propagation loss.

On the contrary, for example, a case will be considered, in which the inclined portion 3600 of the propagation edge 360 is not opposed to the side surface 354 of the waveguide 35, but opposed to a material layer having the same refractive index as that of the buffering portion 50. In this case, the surface plasmon propagating on the portion 3601 of the edge 360 has a wavenumber K_(SP2) that corresponds to the effective refractive index derived from both the higher refractive index n_(WG) of the waveguide 35 and the lower refractive index n_(BF) of the buffering portion 50. Whereas, the surface plasmon propagating on the inclined portion 3600 of the edge 360 has a wavenumber K_(SP1) smaller than wavenumber K_(SP2) because the plasmon antenna perceives only the lower refractive index n_(BF) of the buffering portion 50 due to the absence of the waveguide 35 in the vicinity.

Furthermore, in the configuration of the present invention, by appropriately choosing the above-described first and second distances D_(WN1) and D_(WN2), desired light use efficiency can be achieved in the near-field light generating element. Here, the first distance D_(WN1) denotes a distance between the inclined portion 3600 on the end surface 36 a side of the propagation edge 360 and the side surface 3540 of the waveguide 35. And the second distance D_(WN2) denotes a distance between the portion 3601 other than the inclined portion 3600 of the propagation edge 360 and the side surface 3541 of the waveguide 35. As explained in detail with practical examples later, the first distance D_(WN1) is preferably 46% or more of the second distance D_(WN2), and 160% or less of the second distance D_(WN2). Further, the difference (D_(WN1)-D_(WN2)), which is the result of subtracting the second distance D_(WN2) from the first distance D_(WN1), is preferably −80 nm or more, and +90 nm or less. By setting the distances D_(WN1), and D_(WN2) so as to meet such conditions, as explained in detail with practical examples later, the difference between the wavenumber K_(SP2) of the surface plasmon propagating on the portion 3601 of the edge 360 and the wavenumber K_(SP1) of the surface plasmon propagating on the inclined portion 3600 of the edge 360 falls within a predetermined range. Here, a part of the surface plasmon is converted into an electromagnetic wave getting away from the propagation edge during moving from the portion 3601 of the propagation edge 360 to the inclined portion 3600 of the edge 360. Then, the above-described setting of the distances D_(WN1) and D_(WN2) enables the energy loss by the conversion to be limited within an allowable range. As a result, the light use efficiency of the near-field light generating element can be 10% or more, the near-field light generating element including the waveguide 35, the buffering portion 50 and the plasmon antenna 36.

Furthermore, the length (L_(BF1)+L_(BF2)) of the whole buffering portion 50, that is, the portion through which the waveguide 35 and the surface plasmon antenna 36 are coupled with each other in a surface plasmon mode, is preferably larger than the wavelength λ_(L) of the laser light 53. In this preferable case, the coupled portion has an area markedly larger than a so-called “focal region” in the case that, for example, laser light is converged on a buffering portion 50 and a surface plasmon antenna 36 and coupled in a surface plasmon mode. Therefore, the configuration quite different from the system including such “focal region” can be realized in the present invention; and thus, very stable coupling in the surface plasmon mode can be achieved. The induction of surface plasmon mode is disclosed in, for example, Michael Hochberg, Tom Baehr-Jones, Chris Walker & Axel Scherer, “Integrated Plasmon and dielectric waveguides”, OPTICS EXPRESS Vol. 12, No. 22, pp 5481-5486 (2004), US patent Publication No. 2005/0249451 A1, and U.S. Pat. No. 7,330,404B2.

FIGS. 7 a to 7 d show schematic views illustrating various embodiments regarding the shape and arrangement of the near-field light generating element (the waveguide, the buffering portion and the surface plasmon antenna) and the main magnetic pole according to the present invention.

Referring to FIG. 7 a, a main magnetic pole 70 is one layer extending parallel to the element-formation surface 2202. A portion of a surface plasmon antenna 71 on the head part end surface 2210 side is inclined with respect to the element-formation surface 2202 so as to become closer to the end of the main magnetic pole 70 on the head part end surface 2210 side toward the head part end surface 2210. In addition, the side surface 724 of a waveguide 72 extends, along the surface plasmon antenna 71 (the propagation edge 710), to the neighborhood of the near-field light generating end surface 71 a of the surface plasmon antenna 71. That is, a portion on the end surface 71 a side of the side surface 724 is opposed to the propagation edge 710 of the surface plasmon antenna 71 with a predetermined distance. In this embodiment, the distance D_(W-P)′ between the waveguide 72 and the main magnetic pole 70 in Z-axis direction can be set to a sufficiently large value while the near-field light generating end surface 71 a of the surface plasmon antenna 71 is positioned near the end surface 70 e of the main magnetic pole 70, on the head part end surface 2210. Resultantly, there can be more reliably avoided such a situation in which a part of the laser light is absorbed into the main magnetic pole and the amount of light to be converted into the near-field light is reduced.

In the embodiment shown in FIG. 7 b, a main magnetic pole 74, a surface plasmon antenna 75, a buffering portion 76, and a waveguide 77 are sequentially stacked toward +Z direction, starting from the slider substrate 220 side. A propagation edge 750 for causing surface plasmon to propagate thereon is positioned on the side opposite to the main magnetic pole 74 in the surface plasmon antenna 75, and extends to the near-field light generating end 75 a. Consequently, the near-field light generating end 75 a is located in the trailing side (+Z side) of the end surface 74 e of the main magnetic pole 74, on the head part end surface 2210. In addition, the side surface 774 of the waveguide 77 extends, along the surface plasmon antenna 75 (the propagation edge 750), to the neighborhood of the near-field light generating end surface 75 a of the surface plasmon antenna 75. That is, a portion on the end surface 75 a side of the side surface 774 is opposed to the propagation edge 750 of the surface plasmon antenna 75 with a predetermined distance. Also in this embodiment, the near-field light generating end 75 a can be positioned sufficiently near the end surface 74 e of the main magnetic pole 74, and write field having a sufficiently large gradient can be applied to a sufficiently heated portion of the magnetic recording layer of a magnetic disk.

In the embodiment shown in FIG. 7 c, the configuration of a waveguide 35, a surface plasmon antenna 36 and a main magnetic pole layer 340 is the same as that shown in FIGS. 3 and 4. However, a write shield layer 79, which is a return yoke for receiving a magnetic flux returned from a magnetic disk, is provided in the side opposite to the main magnetic pole layer 340 in relation to the waveguide 35 and surface plasmon antenna 36, that is, in the leading side (in −Z side) of the waveguide 35 and surface plasmon antenna 36. The write shield layer 79 and the main magnetic pole layer 340 are magnetically connected with each other through a back contact portion 78. Further, a write coil layer 343′ is formed so as to pass through in one turn at least between the main magnetic pole layer 340 and the write shield layer 79, and has a spiral structure with the back contact portion 78 as a center. Also in this embodiment, favorable thermally-assisted magnetic recording can be performed by using the surface plasmon according to the present invention.

In the embodiment shown in FIG. 7 d, a surface plasmon antenna 81 includes: a near-field light generating end 81 a where near-field light is generated; and a propagation surface 810 for propagating surface plasmon excited by laser light propagating through a waveguide 80. The propagation surface 810 may be a planer or curved surface. The side surface 804, which is the upper surface of the waveguide 80, extends to the neighborhood of the near-field light generating end surface 81 a. The side surface 8040 and the propagation edge 8100 are opposed to each other with a predetermined distance, and the side surface 8041 and the propagation edge 8101 are opposed to each other with a predetermined distance, so as for the light propagating through the waveguide 80 to be coupled with the surface plasmon antenna 81 in a surface plasmon mode. Further, also in the present embodiment, the region sandwiched between the side surface 804 and the propagation surface 810 of the surface plasmon antenna 81 becomes a buffering portion 85. The present embodiment also enables favorable thermally-assisted magnetic recording with use of the surface plasmon according to the present invention.

Alternatively, configurations in which the surface plasmon antennas 71, 75 and 36 include propagation surfaces opposed to the side surfaces of the waveguides 72, 77 and 35, instead of the propagation edges 710, 750 and 360, respectively, are within the scope of the present invention.

FIG. 8 shows a block diagram illustrating the circuit structure of the recording/reproducing and light-emission control circuit 13 of the magnetic disk apparatus shown in FIG. 1.

In FIG. 8, reference numeral 90 indicates a control LSI, 91 indicates a write gate for receiving recording data from the control LSI 90, 92 indicates a write circuit, 93 indicates a ROM that stores a control table or the like for controlling the value of drive current supplying to the laser diode 40, 95 indicates a constant current circuit for supplying sense current to the MR element 33, 96 indicates an amplifier for amplifying the output voltage from the MR element 33, 97 indicates a demodulator circuit for outputting reproduced data to the control LSI 90, 98 indicates a temperature detector, and 99 indicates a control circuit for controlling the laser diode 40, respectively.

The recording data outputted from the control LSI 90 is supplied to the write gate 91. The write gate 91 supplies recording data to the write circuit 92 only when a recording control signal outputted from the control LSI 90 instructs a write operation. The write circuit 92 applies write current according to this recording data to the write coil layer 343, and then a write operation is performed onto the magnetic disk by write field generated from the main magnetic pole 3400.

A constant current flows from the constant current circuit 95 into the MR multilayer 332 only when the reproducing control signal outputted from the control LSI 90 instructs a read operation. The signal reproduced by the MR element 33 is amplified by the amplifier 96, demodulated by the demodulator circuit 97, and then, the obtained reproduced data is outputted to the control LSI 90.

The laser control circuit 99 receives a laser ON/OFF signal and a drive current control signal, which are outputted from the control LSI 90. When the laser ON/OFF signal is an ON operation instruction, a drive current of an oscillation threshold value or more flows into the laser diode 40. Thereby, the laser diode 40 emits light; then the laser light propagates through the waveguide 35 and couples with the surface plasmon antenna 36 in the surface plasmon mode. As a result, near-field light is generated from the end of the surface plasmon antenna 36, reaches the magnetic recording layer of the magnetic disk, and heats the magnetic recording layer. The value of drive current in this occasion is controlled to a value corresponding to the drive current control signal. The control LSI 90 generates the laser ON/OFF signal with its timing adjusted according to recording/reproducing operations, and determines the value of drive current control signal, by referring the temperature value in the magnetic recording layer of the magnetic disk or the like, which is measured by the temperature detector 98, based on the control table in the ROM 93. The control table may include data about the relation between the drive current value and the mount of temperature increase by thermal-assist operation in the magnetic recording layer, and data about the temperature independence of the anisotropic field (coercive force) of the magnetic recording layer, as well as the temperature dependences of the oscillation threshold and the characteristics of light output vs. drive current. Thus, it is possible to realize not only a current application to the laser diode 40 linked simply with the recording operation but also more diversified current application modes, by providing the system of the laser ON/OFF signal and drive current control signal independently from the recording/reproducing control signal system.

Obviously, the circuit structure of the recording/reproducing and light-emission control circuit 13 is not limited to that shown in FIG. 8. It is also possible to specify write and read operations by using a signal other than the recording control signal and reproducing control signal.

Practical examples will be described below, in which the generation of near-field light in a near-field light generating element (including a surface plasmon antenna, a buffering portion and a surface plasmon antenna) according to the present invention was analyzed by simulation, and a thermally-assisted magnetic recording was performed to a magnetic recording medium with use of a head provided with the near-field light generating element.

An experiment for the simulation analysis was conducted by using a three-dimensional Finite-Difference Time-Domain (FDTD) method, which is an electromagnetic field analysis technique. The simulation analysis experiment was conducted on a system which was an area including: a head part 221 including a waveguide 35, a buffering portion 50, a surface plasmon antenna 36, a main magnetic pole 3400, and an overcoat layer 38; and an air layer (with a refractive index n=1) covering the head part end surface 2210, shown in FIGS. 4 and 5. Laser light entering the waveguide 35 was a Gaussian beam with a wavelength λ_(L) of 650 nm, having TM polarization (in which the oscillation direction of electric field of the laser light is perpendicular to the layer surface of the waveguide 35, that is, in Z-axis direction). The intensity I_(IN) of the laser light was 655 (V/m)².

The waveguide 35 had a width W_(WG2) (FIG. 4) of 0.8 μm and a thickness T_(WG) of 0.25 μm, and was formed of Ta₂O₅ (with a refractive index n=2.15). The surface plasmon antenna 36 had a width W_(NF) (FIG. 4) of 0.85 μm and a thickness T_(NF1) of 0.3 μm, and was formed of Ag (in which the real part of the refractive index was 0.134, and the imaginary part was 4.135). In the surface plasmon antenna 36, the distance D_(BF) (FIG. 4) between the head part end surface 2210 and the position from which the surface plasmon antenna 36 begins to taper was 0.7 μm, and the whole length H_(NF) was 2.5 μm. The apex angle θ_(NF) (FIG. 5) of the apex 360 a in the near-field light generating end surface 36 a was 110° (degrees), and the height T_(NF2) (FIG. 5) was 20 nm. Further, the distance D_(N-P) (FIG. 5) on the end surface 2210 between the end surface 36 a and the end surface 3400 e of the main magnetic pole 3400 was 50 nm. The overcoat layer 38 was formed of Al₂O₃ (with a refractive index n=1.65), and the buffering portion 50 was a portion of the overcoat layer 38. That is, the refractive index n_(BF) of the buffering portion 50 was 1.65. The end surface 3400 e (FIG. 5) of the main magnetic pole 3400 had a shape of a trapezoid having a short-edge length of 100 nm on the surface plasmon antenna 36 side, a long-edge length of 195 nm on the opposite side, and a height of 300 nm. The main magnetic pole 3400 was formed of FeCo (in which the real part of the refractive index was 2.87, and the imaginary part was 3.63).

(Relationship Between the First and Second Distances and the Light Use Efficiency)

Under the experimental conditions described above, the relationship between the first and second distances D_(WN1) and D_(WN2) (FIG. 4) and the light use efficiency of the near-field light generating element was determined by simulation. Here, the first and second distances D_(WN1) and D_(WN2) are distances between the side surface 354 of the waveguide 35 and the propagation edge 360 of the surface plasmon antenna 36. And the light use efficiency of the near-field light generating element is given by I_(OUT)/I_(IN) (×100), where I_(IN) is the intensity of laser light 53 incident to the waveguide 35, and I_(OUT) is the intensity of near-field light emitted from the near-field light generating end surface 36 a after converting the laser light into surface plasmon in the surface plasmon antenna 36.

Running-off distances by which the laser light incident with intensity of I_(IN) ran off from the side surface of the waveguide 35 (with its width W_(WG2)=0.8 μm and its thickness T_(WG)=0.25 μm) were calculated to be −51 nm in the width W_(WG2) direction, and +86 nm in the thickness T_(WG) direction. The running-off distance is defined as a distance, in one direction from the side surface of the waveguide 35, of the position at which the intensity of running-off light is reduced to e⁻² (e: base of natural logarithm) of the intensity I_(IN) as a standard. Therefore, the running-off distance of −51 nm in the width W_(WG2) direction shows that the position at which the light intensity is reduced to e⁻² belongs within the waveguide 35. From those, the ratio of the energy that a part of the incident laser light located within the waveguide 35 has, so-called the filling factor, was calculated to be 0.812; as a result, the effective refractive index was 1.92.

Table 1 shows the result of the determinations by the simulation of the relationship between the first and second distances D_(WN1) and D_(WN2) (FIG. 4) and the light use efficiency. Further, FIG. 9 shows a graph illustrating the relationship between the first and second distances D_(WN1) and D_(WN2) and the light use efficiency shown in Table 1. Here, the first distance D_(WN1) denotes a distance between the inclined portion 3600 on the near-field light generating end surface 36 a side of the propagation edge 360 and the side surface 3540 of the waveguide 35. And the second distance D_(WN2) denotes a distance between the portion 3601 other than the inclined portion 3600 of the propagation edge 360 and the side surface 3541 of the waveguide 35.

TABLE 1 The first distance 0 50 100 150 200 250 300 D_(WN1) (nm) The second 150 150 150 150 150 150 150 distance D_(WN2) (nm) D_(WN1) − D_(WN2) (nm) −150 −100 −50 0 +50 +100 +150 D_(WN1)/D_(WN2) 0 0.333 0.667 1 1.333 1.667 2 NF light intensity 8.0 32.5 88.4 91 88.4 55.4 25.0 ((V/m)²) Light use 1.2 5.0 13.5 13.9 13.5 8.5 3.8 efficiency (%)

Referring to Table 1 and FIG. 9, in the case that the difference (D_(WN1)-D_(WN2)), which is the result of subtracting the second distance D_(WN2) from the first distance D_(WN1), is −80 nm or more, and +90 nm or less, the light use efficiency of 10% or more is obtained, which is required for achieving favorable thermally-assisted magnetic recording in the manufacturing field of the heads. That is, the light use efficiency of 10% or more is obtained if the first distance D_(WN1) is 46% or more of the second distance D_(WN2), and 160% or less of the second distance D_(WN2). The setting of the distances D_(WN1) and D_(WN2) to meet the above-described conditions enables the difference between the wavenumber K_(SP2) of the surface plasmon propagating on the portion 3601 of the propagation edge 360 and the wavenumber K_(SP1) of the surface plasmon propagating on the inclined portion 3600 of the edge 360 falls within a predetermined range. Here, a part of the surface plasmon is converted into an electromagnetic wave getting away from the propagation edge during moving from the portion 3601 of the edge 360 to the inclined portion 3600 of the edge 360. Then, the above-described setting of the distances D_(WN1) and D_(WN2) enables the energy loss by the conversion to be limited within an allowable range. Accordingly, it is understood that: the first distance D_(WN1) is preferably 46% or more of the second distance D_(WN2), and 160% or less of the second distance D_(WN2); and the difference (D_(WN1)-D_(WN2)), which is the result of subtracting the second distance D_(WN2) from the first distance D_(WN1), is preferably −80 nm or more, and +90 nm or less.

(Thermally-Assisted Magnetic Recording with Use of a Bit-Patterned Medium)

Hereinafter, a practical example will be described below, in which a thermally-assisted magnetic recording was performed to a bit-patterned medium by simulation, with use of a thermally-assisted magnetic recording head provided with the near-field light generating element used in the above-described practical examples.

FIGS. 10 a and 10 b show a cross-sectional view and a top view, respectively, schematically illustrating the structure of the bit-patterned medium used in the practical example.

As shown in FIGS. 10 a and 10 b, the bit-patterned medium 100 used in the practical example included: a number of dots 1001 for constituting record bits, formed on a glass substrate 1000; and a protective film 1002 formed on the glass substrate 1000 so as to cover the dots 1001. Each dot 1001 was formed of a multilayer of (Co(0.3 nm)/Pd(0.7 nm))×20 layers. The protective film 1002 was formed of C (carbon). The magnetic anisotropy energy K_(U) of the bit-patterned medium 100 was 1.0×10⁶ J/m³ (1.0×10⁷ erg/m³) at room temperature, and the saturation magnetic flux density was approximately 500 emu/cc at room temperature. The coercive force H_(C) of the bit-patterned medium 100 was 20 kOe (oersteds) at 50° C., 14 kOe at 150° C., 7 kOe at 300° C., and 0 kOe at approximately 400° C. (=T_(C)). Further, in FIG. 10 b, the size (diameter) of the dot 1001 was approximately 20 nm, and the pitch (distance) between adjacent dots 1001 was approximately 30 nm.

Then, a thermally-assisted magnetic recording was performed to the above-described bit-patterned medium 100 by simulation, with use of the above-described thermally-assisted magnetic recording head. The result is that the temperature of a portion to be written of the bit-patterned medium 100 increased by approximately 300° C. From the result, it has been shown that the thermally-assisted magnetic recording can be achieved on the bit-patterned medium with dot size of 20 nm.

As described above, it is understood that a near-field light generating element is provided, in which reduced is the propagation loss of excited surface plasmon that propagates to the near-field light generating end, and thus the light use efficiency is improved. Further, it is also understood that provided is a thermally-assisted magnetic recording head capable of appropriately heating the write position on the magnetic recording medium. Accordingly, the present invention can achieve favorable thermally-assisted magnetic recording, and contribute to the achievement of higher recording density, for example, exceeding 1 Tbits/in².

All the foregoing embodiments are by way of example of the present invention only and not intended to be limiting, and many widely different alternations and modifications of the present invention may be constructed without departing from the spirit and scope of the present invention. Especially, the near-field light generating element utilizing the surface plasmon mode according to the present invention can be applied to optical devices with greatly minute optical paths such as ultra-high-speed light modulation devices. Accordingly, the present invention is limited only as defined in the following claims and equivalents thereto. 

1. A near-field light generating element comprising: a waveguide through which a light for exciting surface plasmon propagates; and a plasmon antenna comprising: a near-field light generating end for emitting near-field light; and a propagation surface or a propagation edge for causing surface plasmon excited by the light to propagate thereon, extending to said near-field light generating end, wherein an inclined portion of said propagation surface or said propagation edge on the near-field light generating end side extends so as to become closer to an end surface of said plasmon antenna toward said near-field light generating end, said end surface being on a side opposite to said propagation surface or said propagation edge, and a side surface of said waveguide extending to a neighborhood of said near-field light generating end, and a portion of said side surface on the near-field light generating end side being opposed to said propagation surface or said propagation edge with a predetermined distance so as for the light propagating through said waveguide to be coupled with said plasmon antenna in a surface plasmon mode.
 2. The near-field light generating element as claimed in claim 1, wherein a first distance is 46 percent or more of a second distance, and 160 percent or less of the second distance, where the first distance denotes a distance between said inclined portion of said propagation surface or said propagation edge on the near-field light generating end side and said side surface of said waveguide, and the second distance denotes a distance between the portion other than said inclined portion of said propagation surface or said propagation edge and said side surface of said waveguide.
 3. The near-field light generating element as claimed in claim 1, wherein a difference that is a result of subtracting a second distance from a first distance is −80 nanometers or more, and +90 nanometers or less, where the first distance denotes a distance between said inclined portion of said propagation surface or said propagation edge on the near-field light generating end side and said side surface of said waveguide, and the second distance denotes a distance between the portion other than said inclined portion of said propagation surface or said propagation edge and said side surface of said waveguide.
 4. The near-field light generating element as claimed in claim 1, wherein said plasmon antenna is formed of one element selected from a group of Pd, Pt, Rh, Ir, Ru, Au, Ag, Cu or Al, or an alloy made of at least two selected from the group.
 5. The near-field light generating element as claimed in claim 1, wherein said propagation surface or said propagation edge is covered with a material having a refractive index equal to or higher than a refractive index of a material covering a surface of said plasmon antenna, said surface being opposite to said propagation surface or said propagation edge.
 6. The near-field light generating element as claimed in claim 1, wherein a portion sandwiched between a portion of said side surface of said waveguide on the near-field light generating end side and said propagation surface or said propagation edge is a buffering portion having a refractive index lower than a refractive index of said waveguide.
 7. The near-field light generating element as claimed in claim 6, wherein said buffering portion is a portion of an overcoat layer formed so as to cover said waveguide.
 8. A thermally-assisted magnetic recording head comprising: a magnetic pole for generating write field from its end on an opposed-to-medium surface side; a waveguide through which a light for exciting surface plasmon propagates; and a plasmon antenna comprising: a near-field light generating end for emitting near-field light, reaching the opposed-to-medium surface; and a propagation surface or a propagation edge for causing surface plasmon excited by the light to propagate thereon, extending to said near-field light generating end, a side surface of said waveguide extending to a neighborhood of said near-field light generating end, and a portion of said side surface on the near-field light generating end side being opposed to said propagation surface or said propagation edge with a predetermined distance so as for the light propagating through said waveguide to be coupled with said plasmon antenna in a surface plasmon mode.
 9. The thermally-assisted magnetic recording head as claimed in claim 8, wherein said waveguide is provided in a side opposite to said magnetic pole in relation to said plasmon antenna.
 10. The thermally-assisted magnetic recording head as claimed in claim 9, wherein a portion on the opposed-to-medium surface side of said plasmon antenna is inclined so as to become closer to an end portion on the opposed-to-medium surface side of said magnetic pole toward the opposed-to-medium surface.
 11. The thermally-assisted magnetic recording head as claimed in claim 9, wherein a portion on the opposed-to-medium surface side of said magnetic pole is inclined so as to become closer to an end portion on the opposed-to-medium surface side of said plasmon antenna toward the opposed-to-medium surface.
 12. The thermally-assisted magnetic recording head as claimed in claim 8, wherein an inclined portion of said propagation surface or said propagation edge on the near-field light generating end side extends so as to become closer to an end surface of said plasmon antenna toward said near-field light generating end, said end surface being on a side opposite to said propagation surface or said propagation edge, and wherein a first distance is 46 percent or more of a second distance, and 160 percent or less of the second distance, where the first distance denotes a distance between said inclined portion of said propagation surface or said propagation edge on the near-field light generating end side and said side surface of said waveguide, and the second distance denotes a distance between the portion other than said inclined portion of said propagation surface or said propagation edge and said side surface of said waveguide.
 13. The thermally-assisted magnetic recording head as claimed in claim 8, wherein an inclined portion of said propagation surface or said propagation edge on the near-field light generating end side extends so as to become closer to an end surface of said plasmon antenna toward said near-field light generating end, said end surface being on a side opposite to said propagation surface or said propagation edge, and wherein a difference that is a result of subtracting a second distance from a first distance is −80 nanometers or more, and +90 nanometers or less, where the first distance denotes a distance between said inclined portion of said propagation surface or said propagation edge on the near-field light generating end side and said side surface of said waveguide, and the second distance denotes a distance between the portion other than said inclined portion of said propagation surface or said propagation edge and said side surface of said waveguide.
 14. The thermally-assisted magnetic recording head as claimed in claim 8, wherein said plasmon antenna is formed of one element selected from a group of Pd, Pt, Rh, Ir, Ru, Au, Ag, Cu or Al, or an alloy made of at least two selected from the group.
 15. The thermally-assisted magnetic recording head as claimed in claim 8, wherein said propagation surface or said propagation edge is covered with a material having a refractive index equal to or higher than a refractive index of a material covering a surface of said plasmon antenna, said surface being opposite to said propagation surface or said propagation edge.
 16. The thermally-assisted magnetic recording head as claimed in claim 8, wherein a portion sandwiched between a portion of said side surface of said waveguide on the near-field light generating end side and said propagation surface or said propagation edge is a buffering portion having a refractive index lower than a refractive index of said waveguide.
 17. The thermally-assisted magnetic recording head as claimed in claim 16, wherein said buffering portion is a portion of an overcoat layer formed so as to cover said waveguide.
 18. The thermally-assisted magnetic recording head as claimed in claim 8, wherein a thermal conduction layer is provided between said plasmon antenna and said magnetic pole, so as to cover an end surface of said plasmon antenna, said surface being opposite to said propagation surface or said propagation edge.
 19. A head gimbal assembly comprising: a thermally-assisted magnetic recording head as claimed in claim 8; and a suspension supporting said thermally-assisted magnetic recording head.
 20. A magnetic recording apparatus comprising: at least one head gimbal assembly comprising a thermally-assisted magnetic recording head and a suspension supporting said thermally-assisted magnetic recording head; at least one magnetic recording medium; and a recording circuit for controlling write operations which said thermally-assisted magnetic recording head performs to said at least one magnetic recording medium, said thermally-assisted magnetic recording head comprising: a magnetic pole for generating write field from its end on an opposed-to-medium surface side; a waveguide through which a light for exciting surface plasmon propagates; and a plasmon antenna comprising: a near-field light generating end for emitting near-field light, reaching the opposed-to-medium surface; and a propagation surface or a propagation edge for causing surface plasmon excited by the light to propagate thereon, extending to said near-field light generating end, a side surface of said waveguide extending to a neighborhood of said near-field light generating end, and a portion of said side surface on the near-field light generating end side being opposed to said propagation surface or said propagation edge with a predetermined distance so as for the light propagating through said waveguide to be coupled with said plasmon antenna in a surface plasmon mode, and said recording circuit further comprising a light-emission control circuit for controlling operations of a light source that generates the light for exciting surface plasmon. 